I've build a series of keywords and solved the problem.
Here is the solution that I've implemented:
A weekly keyword in order to get all the days except weekends:
A Group keyword in order to take out the free days(like holidays) and obtain only the office days:
A Monthly keyword for the 1st day from the month:
A Roll keyword in order to get the 1st working day to raport to it:
Another Roll keyword that will be used to add the delayed number of days:
For example if I need to postpone the executions days with two days, I will adjust it to +2
The keyword used to schedule jobs on the 3rd working day is:
and the result is :
If the closing dates are postopned with 2 days, then from D keyword adjusting it with 2 (+2) the result will be:
Thank you Pete and Wolfgang for your support!